Highly alkaline cleaning agents are well known for their applicability in institutional and household dishwashing machines. The highly alkaline cleaners commonly contain constituents that can act to prevent deposition of or act to remove inorganic salt residues, can act to clean dishes of organic or bio-organic food residues, and can act to destain. The greater amount of cleaning compositions consumed consist of solid cleaners. However, the use of liquid cleaners has generated substantial interest in recent years because of the many advantages of liquid detergents. Caustic dusts that are generated by solids which can cause personal health problems are absent in liquids. Liquid cleaners can be injected into closed systems in accurate, precise measured doses. Liquid cleaners are homogeneous, require no heat of dissolution, and are substantially instantly solubilized, an important factor in low temperature cleaning. Liquid cleaners can exist in solution form or as a suspension, slurry or emulsion.
The production of highly concentrated liquid cleaners is a desired goal since a more concentrated cleaner can be handled economically in smaller containers, less water can be consumed in manufacture, and can be relied on to deliver to the wash water effective amounts of alkaline cleaning agents. We have found, however, that there can be limits under certain conditions upon the concentration of cleaning materials that can be attained in stable aqueous solutions or suspensions. In many cases, less than 15 wt-% of sodium cleaners in a mixture of sodium condensed phosphate hardness sequestering agent and sodium hydroxide can be maintained in aqueous solution. In concentrated cleaners in the form of an emulsion, thickeners can be needed in the cleaner, and substantial limits on the amount of hardness sequestering agent and base can occur. The consequence of exceeding the concentration limits of these cleaners is the production of unstable emulsions which upon storage can result in the precipitation or separation of solids. The use of a separated liquid cleaner can result in the introduction into the wash water of very low concentrations of cleaner or can result in plugging and clogging of pump lines and filters by the presence of substantial amounts of precipitated solids.
One method of forming a stable solution or suspension of concentrated highly alkaline cleaners is to use a polyelectrolyte thickening agent such as sodium polyacrylate or polyacrylic acid. Sabatelli et. al., U.S. Pat. Nos. 3,671,440 and 4,147,650 both teach liquid warewashing cleaners formulated with alkali metal hydroxide, alkali metal pyrophosphate, alkali metal hypochlorite, sodium or potassium condensed phosphate, and other inorganic cleaners in combination with a polyelectrolyte thickener such as polyacrylic acid, polyacrylate, polyacrylamide, etc. We have found, however, that the presence of organic polyelectrolytes in the system containing available chlorine can be a substantial drawback. The available chlorine can interact and degrade the organic polyelectrolyte, polyacrylate, resulting in both the consumption of available chlorine which is essential for destaining properties, and the destabilization of the emulsion which relies on the polyacrylate thickener for stability. We have also found that many other organic and inorganic thickening agents are unsatisfactory in forming stable alkaline liquid emulsions. Further, in certain systems as much as 10 wt-% of the organic polyelectrolyte may be necessary in order to form a stable emulsion.
Accordingly, a substantial need exists for a highly alkaline liquid cleaner composition having cleaning, water treating and destaining properties in the form of a stable emulsion having a thickener which does not interact with the source of chlorine.